I am currently playing around a bit with Firefox addons.
To create a GUI for such extensions you need XUL, a XML-based markup language.
Now, check out the namespace for XUL:
http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul
Don’t get it? Fool! Go watch Ghostbusters I again! (Man, this reminds me of me being a kid and watching this movie over and over again).
However, now guess how a Firefox addon is called for debugging JavaScript in such extensions. Right: Venkman
